This invention relates to a two-way automatic communications system or TWACS, and more particularly, to a method for reliably detecting signals transmitted from the location of an electricity user during a fast poll of electrical meters connected in a power distribution system employing TWACS.
TWACS technology, various aspects of which are described, for example, in U.S. Pat. Nos. 6,940,396, 5,933,072, 5,486,805, 5,262,755, 4,963,853, 4,918,422, and 4,914,418, has been primarily used for reading electrical meters connected in a power distribution system, even though TWACS protocols have also been developed to support other features such as fast polling of the meters. A major advantage of fast polling is that it quickly allows a utility to test for the presence or absence of a large number of meters which, in turn, is advantageous in that it allows the utility to determine and map the extent of power outages within the system. When a TWACS is operating in a fast poll response mode, much of the overhead information included in other message packets sent through the TWACS is eliminated, with the result that a response to a query signal sent to the meters can be reduced to only one byte.
As originally designed, in the fast poll mode, only one byte is transmitted from a meter, and this byte contains known data. The inbound receiver of the TWACS would then compare the received bits against the known data to determine whether a particular meter actually responded or “talked” in response to a query signal. Some meters currently installed in existing systems do not fully support the fixed fast poll mode, but instead transmit 4 known bits and 4 unknown bits. In order to support those users as well as those employing more current meters, the present invention includes a method for estimating the unknown bits for meters that use the older, fast poll response method.
In the fast poll mode, if a meter does not respond, ostensibly because of a power outage at that meter's location, the inbound receiver of the TWACS will be processing only noise. Comparing data containing only noise to a known 8-bit pattern still has a 0.4% chance of being correct, which is unacceptably high. For this reason, the present invention is directed to a detection method which attempts to determine the presence or absence of a signal with high accuracy, and is designed to function with either 4 known bits or 8 known bits.